This invention relates generally to the field of wireless communications, and particularly to a system and method for communicating with, and for monitoring the location and other environmental characteristics of, a Global Positioning System (GPS) receiver.
The Department of Defense developed the Global Positioning System (GPS) to accurately determine the location of a receiver near the surface of the earth. The GPS employs a constellation of 24 satellites that currently orbit the earth. These satellites were developed and built by the assignee of the present invention. These satellites serve as reference points and send radio signals that include information regarding the satellites"" position, orbit and GPS time. A GPS receiver on the earth""s surface can detect this information and, based on this information, can determine its position relative to the satellites. Therefore, GPS enables users anywhere in the world to determine their locations precisely by using a GPS receiver to interpret signals from the array of satellites. For example, GPS is used by military aircraft, commercial aircraft, trucking fleets, firefighters, law enforcement organizations, as well as by farmers, fishermen, hikers, and private pilots to fix locations and pinpoint targets. To many recreational users, GPS has increased the safety of many recreational pursuits by providing boaters, hikers, skiers, and others who are lost or in trouble with the ability to accurately pin-point their locations and to assist them in navigating their way out of trouble.
Presently, GPS receivers are embodied only in discrete end products, such as, simple hand-held receivers, navigation systems, and surveying equipment. These end products can be carried by the users or attached to the objects to be navigated or under surveillance. Some of these presently-available GPS receivers are even capable of transmitting basic distress or other signals that are accompanied by signals representing the location of the receiver. However, presently-available GPS receivers are still not able to engage in a more comprehensive dialog with a remote station to exchange location and other pertinent information. For example, presently-available GPS receivers cannot be interrogated by a remote station at a regular time interval, or at predetermined times, to determine the specific location of the GPS receiver. In addition, presently-available GPS receivers typically operate on a conventional RF (radio frequency) basis, and therefore cannot communicate in any manner with a remote station if the GPS receiver is out-of-range. In addition, presently-available GPS receivers do not communicate other information, such as variable and known environmental conditions, to other remote stations.
Accordingly, there remains a need for a system and method that allows a remote station to maintain active communication with a GPS receiver, as well as to monitor the location, the environmental measurements, and other related data of the GPS receiver.
The field unit for use in a GPS system provides for a system and method for communicating location and other related information of a field unit to a remote base station. The field unit generates position signals based on signals received from communication with a plurality of GPS satellites. These position signals are transmitted to a remote base station, where they are processed and displayed.
In accordance with one aspect of the field unit, the field unit includes an environmental circuit having devices for determining an environmental condition and producing an environmental signal representative of the environmental condition such as ambient temperature, altitude, pressure and/or humidity. Environmental conditions may also include physical characteristics of a living individual, such as a person or an animal, carrying the field unit. The environmental signal is also transmitted to the remote base station for processing and display. The environmental signal can contain variable information if the environmental condition is a changing condition, or can contain known or predetermined information.
In accordance with another aspect of the field unit, the field unit is capable of communicating information to the remote base station even if the field unit is outside the RF transmission range. The field unit is provided with a cellular link circuit for transmitting the position signals and the environmental signal to the remote base station via a cellular link.
In accordance with yet another aspect of the field unit, the base station interrogates the field unit at predetermined times, or after predetermined time intervals, to cause the field unit to communicate information to the base station. The base station includes an interrogation circuit for generating an interrogation signal, and the field unit includes a receiver for receiving the interrogation signal.
In accordance with a further aspect of the field unit, the field unit is capable of communicating information to the remote base station at predetermined times, or after predetermined time intervals, even without the receipt of an interrogation signal. In this embodiment, the field unit further includes a controller, and a timer coupled to the controller for initiating operation of the field unit. This embodiment is best suited for utilizing an active power management scheme to conserve power.
The field unit can be implemented in the form of a thin strip of mylar-like material for use in low-cost applications. Since the position and environmental signals are processed at the remote base station, minimal processing is performed at the field unit and it can therefore be provided for use in low-cost applications.